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Joelle E Romo, Nathan V Bollar, Coy J Zimmermann, Stephanie G Wettstein
Within the last decade, interest in using biphasic systems for producing furans from biomass has grown significantly. Biphasic systems continuously extract furans into the organic phase, which prevents degradation reactions and potentially allows for easier separations of the products. Several heterogeneous catalyst types, including zeolites, ion exchange resins, niobium-based, and others, have been used with various organic solvents to increase furan yields from sugar dehydration reactions. In this minireview, we summarized the use of heterogeneous catalysts in biphasic systems for furfural and 5-hydroxymethylfurfural production from the past five years, highlighting trends in chemical and physical properties that effect catalytic activity...
November 7, 2018: ChemCatChem
Federica Ruggieri, Luuk M van Langen, Derek T Logan, Björn Walse, Per Berglund
Dynamic kinetic resolution (DKR) reactions in which a stereoselective enzyme and a racemization step are coupled in one pot would represent powerful tools for the production of enantiopure amines through enantioconvergence of racemates. The exploitation of DKR strategies is currently hampered by the lack of effective, enzyme-compatible and scalable racemization strategies for amines. In the present work, the proof of concept of a fully biocatalytic method for amine racemization is presented. Both enantiomers of the model compound 1-methyl-3-phenylpropylamine could be racemized in water and at room temperature using a couple of wild-type, non-proprietary, enantiocomplementary amine transaminases and a minimum amount of pyruvate/alanine as a co-substrate couple...
November 7, 2018: ChemCatChem
Jessica M de Ruiter, Huub J M de Groot, Francesco Buda
When considering water oxidation catalysis theoretically, accounting for the transfer of protons and electrons from one catalytic intermediate to the next remains challenging: correction factors are usually employed to approximate the energetics of electron and proton transfer. Here these energetics were investigated using a closed system approach, which places the catalytic intermediate in a simulation box including proton and electron acceptors, as well as explicit solvent. As a proof of principle, the first two catalytic steps of the mononuclear ruthenium-based water oxidation catalyst [Ru(cy)(bpy)(H2 O)]2+ were examined using Car-Parrinello Molecular Dynamics...
October 23, 2018: ChemCatChem
Oriol Martínez-Ferraté, Christophe Werlé, Giancarlo Franciò, Walter Leitner
A catalytic system based on complexes comprising abundant and cheap manganese together with readily available aminotriazole ligands is reported. The new Mn(I) complexes are catalytically competent in transfer hydrogenation of ketones with 2-propanol as hydrogen source. The reaction proceeds under mild conditions at 80 °C for 20 h with 3 % of catalyst loading using either KO t Bu or NaOH as base. Good to excellent yields were obtained for a wide substrate scope with broad functional group tolerance. The obtained results by varying the substitution pattern of the ligand are consistent with an out-sphere mechanism for the H-transfer...
October 23, 2018: ChemCatChem
Stefan Weber, Julian Brünig, Veronika Zeindlhofer, Christian Schröder, Berthold Stöger, Andreas Limbeck, Karl Kirchner, Katharina Bica
A biphasic process for the hydrogenation of aldehydes was developed using a well-defined iron (II) PNP pincer complex as model system to investigate the performance of various ionic liquids. A number of suitable hydrophobic ionic liquids based on the N(Tf)2 - anion were identified, allowing to immobilize the iron (II) catalyst in the ionic liquid layer and to facilitate the separation of the desired alcohols. Further studies showed that targeted Brønsted basic ionic liquids can eliminate the need of an external base to activate the catalyst...
October 9, 2018: ChemCatChem
Koshiro Nakamura, Akihito Okuda, Kiyotaka Ohta, Hitoshi Matsubara, Kazu Okumura, Kana Yamamoto, Ryosuke Itagaki, Satoshi Suganuma, Etsushi Tsuji, Naonobu Katada
Cobalt-loaded MFI zeolite showed distinct activity for direct methylation of benzene with methane into toluene. High activity was found at around 0.6 of Co/Al molar ratio. Incorporation of carbon from methane into the methyl group of toluene was confirmed with isotope tracer experiments and mass spectroscopy. Ammonia infrared-mass spectroscopy temperature-programmed desorption, transmission electron microscopy, X-ray absorption near edge spectroscopy and extended X-ray absorption fine structure indicated that Lewis acidic divalent (+II of oxidation state) Co species mono-atomically dispersed on the ion exchange site of MFI zeolite was the active species...
September 7, 2018: ChemCatChem
Godwin A Aleku, Christoph Prause, Ruth T Bradshaw-Allen, Katharina Plasch, Silvia M Glueck, Samuel S Bailey, Karl A P Payne, David A Parker, Kurt Faber, David Leys
Fungal ferulic acid decarboxylases (FDCs) belong to the UbiD-family of enzymes and catalyse the reversible (de)carboxylation of cinnamic acid derivatives through the use of a prenylated flavin cofactor. The latter is synthesised by the flavin prenyltransferase UbiX. Herein, we demonstrate the applicability of FDC/UbiX expressing cells for both isolated enzyme and whole-cell biocatalysis. FDCs exhibit high activity with total turnover numbers (TTN) of up to 55000 and turnover frequency (TOF) of up to 370 min-1 ...
September 7, 2018: ChemCatChem
Rolf Sybren Postma, Roger Brunet Espinosa, Leon Lefferts
Nitrite hydrogenation is studied in steady-state as well as transient operation using a Pd catalyst in a tubular membrane contactor reactor. A negative reaction order in hydrogen in steady state operation proofs that hydrogen and nitrite adsorb competitively. In transient operation, feeding nitrite to the Pd surface fully covered with hydrogen results initially in very low conversion of nitrite, speeding up once hydrogen is removed from part of the Pd surface. Additional proof for competitive adsorption between hydrogen and nitrite is provided by the observation that exposure of a nitrite-covered catalyst to hydrogen induces desorption of nitrite...
September 7, 2018: ChemCatChem
Kazuyuki Yasukawa, Fumihiro Motojima, Atsushi Ono, Yasuhisa Asano
Discovery and development of enzymes for the synthesis of chiral amines have been a hot topic for basic and applied aspects of biocatalysts. Based on our X-ray crystallographic analyses of porcine kidney D-amino acid oxidase (pkDAO) and its variants, we rationally designed a new variant that catalyzed the oxidation of ( S )-4-Cl-benzhydrylamine (CBHA) from pkDAO and obtained it by functional high-throughput screening with colorimetric assay. The variant I230A/R283G was constructed from the variant R283G which had completely lost the activity for D-amino acids, further gaining new activity toward ( S )-chiral amines with the bulky substituents...
August 21, 2018: ChemCatChem
Flóra Nagy, Gábor Tasnádi, Diána Balogh-Weiser, Evelin Bell, Mélanie Hall, Kurt Faber, László Poppe
An easy to use method combining the selectivity of metal chelate affinity binding with strong covalent linking was developed for immobilization of non-specific acid phosphatases bearing a His-tag from crude cell lysate. Silica nanoparticles were grafted with aminopropyl functions which were partially transformed further with EDTA dianhydride to chelators. The heterofunctionalized nanoparticles charged with Ni2+ as the most appropriate metal ion were applied as support. First, the His-tagged phosphatases were selectively bound to the metal-chelate functions of the support...
August 21, 2018: ChemCatChem
Stefan Velikogne, Verena Resch, Carina Dertnig, Joerg H Schrittwieser, Wolfgang Kroutil
Imine reductases (IREDs) have recently become a primary focus of research in biocatalysis, complementing other classes of amine-forming enzymes such as transaminases and amine dehydrogenases. Following in the footsteps of other research groups, we have established a set of IRED biocatalysts by sequence-based in silico enzyme discovery. In this study, we present basic characterisation data for these novel IREDs and explore their activity and stereoselectivity using a panel of structurally diverse cyclic imines as substrates...
August 13, 2018: ChemCatChem
Beibei Guo, Douwe S Zijlstra, Johannes G de Vries, Edwin Otten
Water addition to α,β-unsaturated nitriles would give facile access to the β-hydroxy-nitriles, which in turn can be hydrogenated to the γ-amino alcohols. We have previously shown that alcohols readily add in 1,4-fashion to these substrates using Milstein's Ru(PNN) pincer complex as catalyst. However, attempted water addition to α,β-unsaturated nitriles gave the 3-hydroxynitriles in mediocre yields. On the other hand, addition of benzyl alcohol proceeded in excellent yields for a variety of β-substituted unsaturated nitriles...
July 9, 2018: ChemCatChem
Felix Strieth-Kalthoff, Ashley R Longstreet, Jessica M Weber, Timothy F Jamison
Herein, we introduce a new class of bench-stable N -heterocyclic carbene (NHC) nickel-precatalysts for homogeneous nickel-catalysis. The nickel(II) complexes are readily activated to Ni0 in situ under mild conditions, via a proposed Heck-type mechanism. The precatalysts are shown to facilitate carbonyl-ene, hydroalkenylation, and amination reactions.
July 9, 2018: ChemCatChem
Yakub Fam, Thomas L Sheppard, Ana Diaz, Torsten Scherer, Mirko Holler, Wu Wang, Di Wang, Patrice Brenner, Arne Wittstock, Jan-Dierk Grunwaldt
Tomographic imaging of catalysts allows non-invasive investigation of structural features and chemical properties by combining large fields of view, high spatial resolution, and the ability to probe multiple length scales. Three complementary nanotomography techniques, (i) electron tomography, (ii) focused ion beam-scanning electron microscopy, and (iii) synchrotron ptychographic X-ray computed tomography, were applied to render the 3D structure of monolithic nanoporous gold doped with ceria, a catalytically active material with hierarchical porosity on the nm and μm scale...
July 9, 2018: ChemCatChem
Alina Filip, Emma Z A Nagy, Souad D Tork, Gergely Bánóczi, Monica I Toşa, Florin D Irimie, László Poppe, Csaba Paizs, László C Bencze
Tailored mutants of phenylalanine ammonia-lyase from Petroselinum crispum ( Pc PAL) were created and tested in ammonia elimination from various sterically demanding, non-natural analogues of phenylalanine and in ammonia addition reactions into the corresponding ( E )-arylacrylates. The wild-type Pc PAL was inert or exhibited quite poor conversions in both reactions with all members of the substrate panel. Appropriate single mutations of residue F137 and the highly conserved residue I460 resulted in Pc PAL variants that were active in ammonia elimination but still had a poor activity in ammonia addition onto bulky substrates...
June 21, 2018: ChemCatChem
Thierry K Slot, David Eisenberg, Gadi Rothenberg
We consider the factors that govern the activity of bifunctional catalysts comprised of active particles supported on active surfaces. Such catalysts are interesting because the adsorption and diffusion steps, which are often discounted in "conventional" catalytic scenarios, play a key role here. We present an intuitive model, the so-called "active doughnut" concept, defining an active catalytic region around the supported particles. This simple model explains the role of adsorption and diffusion steps in cascade catalytic cycles for active particles supported on active surfaces...
May 24, 2018: ChemCatChem
Filip Sebest, Jay J Dunsford, Matthew Adams, Jeremy Pivot, Paul D Newman, Silvia Díez-González
A series of well-defined copper(I) complexes bearing ring-expanded N-heterocyclic carbene (NHC) ligands has been applied to the azide-alkyne cycloaddition reaction. The obtained results notably showed that the six-membered NHC ligands outperform well-established five-membered ones. [CuI(Mes-6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.
May 9, 2018: ChemCatChem
Dogukan H Apaydin, Hathaichanok Seelajaroen, Orathip Pengsakul, Patchanita Thamyongkit, Niyazi Serdar Sariciftci, Julia Kunze-Liebhäuser, Engelbert Portenkirchner
We report on a self-assembled system comprising a molecular copper-porphyrin photoelectrocatalyst, 5-(4-carboxy-phenyl)-10,15,20-triphenylporphyrinatocopper(II) (CuTPP-COOH), covalently bound to self-organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin-covered TiO2 NTs under cathodic polarization up to -0.3 V vs. Normal hydrogen electrode (NHE) photocatalytically produces H2 O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors...
April 24, 2018: ChemCatChem
Niko M Kinnunen, Matthew Keenan, Kauko Kallinen, Teuvo Maunula, Mika Suvanto
Catalytic combustion of methane, the main component of natural gas, is a challenge under lean-burn conditions and at low temperatures owing to sulfur poisoning of the Pd-rich catalyst. This paper introduces a more sulfur-resistant catalyst system that can be regenerated during operation. The developed catalyst system lowers the barrier that has restrained the use of liquefied natural gas as a fuel in energy production.
April 9, 2018: ChemCatChem
Wouter S Lamme, Jovana Zečević, Krijn P de Jong
The effects of the metal deposition and activation methods on metal particle size and distribution were investigated for carbon nanotube supported Pd catalysts. The Pd precursor was loaded by incipient wetness impregnation, ion adsorption, and deposition precipitation and was activated by thermal treatment under a nitrogen atmosphere or in the liquid phase by reduction by formaldehyde or sodium borohydride. Regardless of the metal precursor loading method, activation under a N2 atmosphere at 500 °C led to homogeneously distributed 4 nm Pd particles...
April 9, 2018: ChemCatChem
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